The present invention relates to a hydraulic drive system for bicycles and the like.
The applicant has proposed a bicycle with a hydraulic transmission disclosed in JP-A2-2043677, a variable displacement hydraulic pump for bicycles disclosed in JP-A2-2043678, an apparatus for controlling eccentricity of an eccentric cam assembly disclosed in JPA2-2043679, a fixed displacement hydraulic motor for driving a bicycle disclosed in JP-A2-2043680, and a bicycle having two drive wheels disclosed in JP-A2-307554.
The bicycle disclosed in JP-A2-2043677 corresponding to U.S. Pat. No. 4,684,143 granted to Yasunori Sato, Aug. 4, 1987 is typical of the above prior art. This bicycle comprises a hydraulic drive system including a variable displacement hydraulic pump driven by a crankshaft through a cam assembly and a fixed displacement hydraulic motor for driving a rear driving wheel provided at input and output portions of the hydraulic drive system, respectively, for driving the bicycle.
The variable displacement hydraulic pump included in a hydraulic drive system comprises a cam assembly consisting of an inner eccentric cam fixed to a crankshaft, and an outer eccentric cam rotatably and eccentrically fitted on the inner eccentric cam. The inner eccentric cam is formed integrally with an inner internal gear having the same center axis as that of the crankshaft. An outer internal gear having the same number of teeth and the same pitch diameter as those of the inner internal gear is arranged to be rotated together with the outer eccentric cam. The outer internal gear is concentrically rotatable relative to the inner internal gear. A center gear is rotatably supported on the center shaft and a fear is rotatably supported on a stationary shaft so that the gear is in mesh with the center gear and one of the inner and outer internal gears. A rocking gear is rotatably supported by a free end of a rocking arm which is rotatably fitted on the center shaft so that the rocking gear is in mesh with the center gear and other of the inner and outer internal gears. Thus, the eccentricity of the eccentric cam assembly can be controlled in a stepless manner by rotating the rocking arm.
In the prior art mentioned above, the variable displacement hydraulic pump combined with the eccentric cam assembly adapted for controlling the eccentricity in a stepless manner is driven by means of a crank mechanism of the bicycle to supply hydraulic oil from the variable displacement hydraulic pump to the fixed displacement hydraulic motor provided at a drive wheel of the bicycle to thereby drive the bicycle.
However, the number of rotations of the pump attained by a person's foot power through the crank mechanism of the bicycle is naturally limited and a capacity of the pump provided at the crank portion of the bicycle is also practically limited. Accordingly, when the drive wheel of bicycle is rotated by the fixed displacement hydraulic motor supplied by the variable displacement hydraulic pump having a limited output, an operating hydraulic pressure to be used becomes high, in particular the hydraulic pressure rises to several hundred kgf/cm.sup.2 at maximum output when the bicycle is driven in an uphill.
The operating hydraulic pressure is desirably as low as possible since a transmitting efficiency of such a hydraulic pump and hydraulic motor intends to decrease as the operating hydraulic presser becomes high. The present invention aims to attain the aforementioned desire.
Furthermore, the prior art mentioned above has a problem that since the variable displacement hydraulic pump is separately constructed from a hanger portion or a bottom bracket of the bicycle and is excessively extended from one side of the bicycle so that the bicycle is unbalanced with respect to the opposite side, and the crank pedals are interfered with during their operation.
Furthermore, in the prior art mentioned above, a hydraulic cylinder including a balancing spring is used as an automatic speed regulator or changer for automatically changing the speed, but the maximum hydraulic pressure for use in such a regulator becomes higher than 1,000 kgf/cm.sup.2 even if the hydraulic pressure is restrained to be as low as possible and therefore a spring having a large size must be used for balancing with the thrust force so that it is difficult to design the regulator in miniature size.